1. Field of the Invention
The present invention relates to a process for preparing a vinyl polymer having a controlled molecular weight and a narrow molecular weight distribution.
2. Description of the Prior Art
Molecular weights and molecular weight distributions of polymers have large influences on properties, such as flow properties, of the polymers. Thus, it is very important to prepare polymers having controlled molecular weights and narrow molecular weight distributions for controlling the properties of the prepared polymers and compositions comprising such the polymers.
A method for the easy preparation of a vinyl polymer having a controlled molecular weight and narrow molecular weight distribution, which is disclosed in J. Am. Chem. Soc., 117, 5614-5615 (1995), Macromolecules, 28, 7901-7910 (1995) and the like, comprises living radically polymerizing a vinyl monomer using an organic halide as a polymerization initiator and a monovalent copper complex which is obtained from a cuprous halide and an electron donating compound such as 2,2'-bipyridyl compounds. This process provides the polymer having the controlled molecular weight and narrow molecular weight distribution when the monomer is styrene, methyl acrylate, etc.
However, the molecular weight distributions of the vinyl polymers prepared by the above process are not still satisfactorily narrow. In particular, the molecular weight distributions of the vinyl polymers are slightly broad when this method is used for polymerizing acrylates (e.g. butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, etc.), or methacrylates (e.g. methyl methacrylate, ethyl methacrylate, etc.).
Accordingly, it has been desired to provide a process for preparing vinyl polymers having narrower molecular weight distributions.